Technical Field
The present subject matter relates to an onboard unit for a vehicular identification system, in particular a road toll, parking space management or access system.
Background Art
A conventional vehicular identification system typically has a data processing centre and, connected thereto, one or more transceivers for communication with onboard units of the abovementioned type which are attached to vehicles passing one of the transceivers of the identification system. Depending on the type of identification system and on the onboard units in use, the transceivers of the identification system can, e.g., be base transceiver stations (BTS) of a cellular phone network and/or short range communication transceivers according to DSRC, WAVE or similar standards.
Such identification systems authorise the use of a toll road or a parking space or the access to a restricted area upon an individual identification of the onboard unit, upon the identification of the vehicle (i.e. its onboard unit or user) being affiliated to an admissible group of vehicles, e.g. a vehicle fleet having access to a restricted area, and/or upon collecting a utilization fee, e.g. a parking or toll fee.
An onboard unit for such vehicular identification systems is generally mounted in the interior of the vehicle, mostly attached to the vehicle's windscreen, and is thereby protected from harsh exterior environmental conditions. Nowadays, an increasing percentage of vehicles is equipped with a windscreen which is coated with metal as an irradiation protector in order to block radiation in the infrared wavelength spectrum of the day light. Furthermore heating wires are often integrated into the glass of the windscreen for defrosting purposes, having a very similar effect as the metallisation of the windscreen: Such wires or metallisation substantially attenuate or even completely block radio communication through the windscreen; the radio communication of onboard units attached thereto is therefore at least prone to errors if not completely inhibited.
A possible remedy thereto is to relocate the antenna of the onboard unit to the outside of the vehicle. This provision requires extra cabling through the car body and reduces the ease and flexibility of use of the onboard unit. Another known solution to said problem is to provide the onboard unit with a weatherproof housing and attach it to the exterior surface of the vehicle, in which case the onboard unit is exposed to tampering and improper use by unauthorised third parties.